1. Field of the Invention
The present invention relates to a method and apparatus for measuring a state of a coil-urging wedge arranged so that a coil inserted in a slot of a stator core of a revolving electric machine represented by a motor or generator can be prevented from extension in the radial direction of a rotor, while the rotor is kept inserted inside the stator.
2. Description of the Related Art
A typical revolving electric machine installed in a power plant is shown in FIG. 31. Revolving electric machine 1 comprises stator core (to be referred to as a core hereinafter) 5 having a plurality of slots 5a in the longitudinal direction (i.e., stacking direction Z), rotor 4 rotatably supported with predetermined gap 6 in the internal space of core 5, and stator coils (to be referred to as coils) 2 respectively inserted in slots 5a. As shown in FIGS. 32 and 33, wedges 3 (=3a and 3b) are inserted in each slot 5a from an axial end portion in the axial direction (Z) to prevent extension of coil 2 in the radial direction (X) from opening 5al formed in a stator wall of slot 5a at a position opposite to rotor 4.
FIGS. 32 and 33 are respectively cross-sectional and longitudinal sectional views for explaining a relationship between slot 5a and wedges 3. As shown in FIG. 33, wedges 3 comprise two kinds of wedges 3a and 3b. Wedges 3a and 3b are inserted alternately in the axial direction X, such that wedge 3a is inserted in slot 5a at a position close to opening 5al, while wedge 3b is inserted therein at a position far from opening 5al. Reference numeral 5b denotes a reaction force reception recess formed at the opening 5al side of each slot 5a. Both end portions of wedge 3a are inserted into recess 5b under pressure. Reference symbol F denotes a coil urging force by wedge fastening; and B, a deflection amount of a wedge when the wedge is urged against the coil.
With the above arrangement, there is a first method of performing a post-assembly test of a coil-urging state of the wedges since a sufficient deflection amount (coil urging force F) is applied to wedge 3a during assembly of the revolving electric machine. According to the first method, when a revolving electric machine is kept operated without inspections for a long period of time, an urging force of wedge 3a against coil 2 is weakened due to some reason, and coil 2 extends from slot 5a and abuts against rotor 4 to cause a decisive accident, i.e., a failure of the revolving electric machine.
In view of the above circumstances, conventionally, a second method has been adopted. According to the second method, a coil-urging state of the wedge is manually inspected by maintenance and inspection personnel periodically, e.g., every several years, by stopping the operation of the revolving electric machine.
In the first method, since the coil-urging state of the wedge is not inspected, reliability for stably supplying power tends to be degraded.
The second method poses the following problem. If a revolving electric machine has a rotor diameter of, e.g., 1,000 mm, a minimum gap between the stator and the rotor is as small as about 15 mm. For this reason, in order to inspect the coil-urging state of wedges 3, after the rotor is removed from the stator, the maintenance and inspection personnel must enter inside the stator and visually check wedges 3 or performs hammering to judge the coil-urging state of wedges 3 by listening to an echo. An inspection operation of wedges 3 by the maintenance and inspection personnel is cumbersome and requires considerable time from the beginning of inspection to its end. In addition, the maintenance and inspection personnel visually checks the wedges or listen to a striking sound or its echo upon hammering. Therefore, the state of wedges 3 which urge coil 2 cannot be objectively judged.